1. Field of the Invention
The invention relates to a controller and control method for a vehicle, which execute shift control over an automatic transmission, and, more particularly, to a technique for shifting an automatic transmission with the use of a shift model.
2. Description of Related Art
There is well known an automatic transmission that includes a plurality of engagement devices, which transmit rotation and torque between an input shaft that receives power from a driving force source and an output shaft that transmits power to drive wheels, and that is shifted by switching between engaged and released states of each of the engagement devices. Generally, in such an automatic transmission, a required value (that is, a control operation amount) of an element (for example, torque, or the like) that is operated for a controlled object is adapted for each gear speed while carrying out evaluations in an actual vehicle, and a shift is carried out using the control operation amount that is determined from a control map obtained in advance for each gear speed on the basis of the adapted result. However, with an increasing number of speeds of an automatic transmission, enormous effort is required for adaptation work, and it is becoming more difficult to employ a mode of shift control based on control maps. Therefore, there is suggested shift model control that is a mode of shift control based on the equation of motion in each of rotating elements that constitute an automatic transmission. In such shift model control, a control operation amount is uniquely determined by solving the equations of motion obtained in advance on the basis of a desired variation mode (shift target value) during shifting, and a shift is carried out using the determined control operation amount. For example, Japanese Patent Application Publication No. 2000-97325 (JP 2000-97325 A) describes a technique for carrying out a shift by, in inertia phase control, setting a target value of an input shaft rotation speed of a transmission as a shift target value and calculating a required value of an engaged-side clutch torque as a control operation amount with the use of a shift model, and a technique for carrying out a shift by setting a target value of an input shaft rotation speed of a transmission and a target value of an output shaft torque of the transmission as shift target values and calculating a required value of an engaged-side clutch torque and a required value of a released-side clutch torque as control operation amounts with the use of a shift model.